1. Field of the Invention
This invention relates to a transparent touch switch of the type which is set at the front side of display devices such as LCDS, CRTS and the like to make switching ON or OFF at an arbitrarily selected position on a display panel using the touch switch.
2. Description of Related Art
Typical of known transparent touch switches is one including transparent upper and lower electrodes which are facing each other through a spacer and can be electrically contacted when one of the electrodes is pressed. In one such switch, the electrodes are formed on glass sheets or plates, respectively. This type of switch is mainly used setting on a display face of an LCD (liquid crystal display device). More particularly, when an operator presses a given position on the transparent switch with the fingers after visual observation, the electrodes at the given position are contacted to turn the switch on.
FIGS. 2 and 3 show this type of known transparent touch switch whereas FIG. 2 shows a non-pressed state of the switch and FIG. 3 shows a pressed state.
In these figures, reference numeral 1 indicates a transparent upper electrode which is made, for example, of ITO and formed on a lower side of a thin upper glass sheet 2 by means such as vapor deposition, sputtering or the like technique. Reference numeral 3 indicates a transparent lower electrode made, for example of ITO and formed on an upper surface of a thick lower glass sheet 4 by a similar technique. The glass sheets 2, 4 are bonded with a spacer 5 while keeping a given space between the sheets 2,4. The spacer 5 is made of a transparent resin and is formed by dispersing spherical fine particles 6 of a resin such as Micro Pearl (available from Sekisui Fine Chemicals Co., Ltd.) in an adhesive 7 such as an epoxy resin and printing the dispersion in the form of dots. Subsequently, the spacer 5 is provided between the paired glass sheets 2,4 and hot-pressed, so that the glass sheets 2,4 are stacked and bonded with the adhesive 7 while keeping the given gap defined by the diameter of the spherical fine particles 6 of the resin.
The resultant transparent touch switch is disposed on a display face, for example, of an LCD (not shown). In operation, while watching the display face, an operator presses a selected portion on the upper glass sheet 2 within the display zone. By this, the pressed portion of the upper glass 2 is partially depressed, as shown in FIG. 3, so that the upper electrode 1 is contacted with the lower electrode 3, causing the switch to turn on. When the press force is removed, the upper glass sheet 2 is returned to the original position shown in FIG. 2 wherein the upper electrode 1 is detached from the lower electrode 3 to make an off state.
Besides, there is also known a transparent touch switch wherein bar-shaped hard particles made of glass fibers are used instead of the spherical resin fine particles and are dispersed in an adhesive material to make a spacer.
However, in the known touch switches where the gap between the paired glass sheets 2,4 is defined with the spherical resin fine particles 6, the spherical resin fine particles 6 are stressed to contain a repulsion force therein at the time of the hot pressing of the spacer 5. The repulsion force may eventually cause the adhesive material 7 to be cracked or broken after the hot-pressing. The cracks or breakage of the adhesive material 7 is disadvantageous in that light is irregularly reflected at the portion where cracked or broken, so that the spacer 5 which should be optically transparent becomes opaque.
With the case where hard fine particles are used instead of the spherical resin fine particles, bar or needle-like hard fine particles are unlikely to pass through a mask mesh, making it difficult to print the dispersion in an amount necessary for the spacer. This will result in stress concentration on the hard fine particles at the time of the hot pressing of the spacer 5, leading to the disadvantage that the particles are broken to cause the portion to be opaque or that the gap between the paired glass sheets is liable to be non-uniform along the sheets.